Process for the production of sulphite liquor



Oct. 6, 1931. M. G. T. SCHROEDER 4 1,826,028

PROCESS FOR THE PRODUCTION OF SULPHITE LIQUOR Filed Feb. 29, 1928 Patented Oct. 6, 1931 I nane rarer "*T IYIA-X GEORG- THEODOR SCHBOEDER, F BER- LIN, GEB-IJZAIIY PROCESS FOR THE PRODUCTION OF SULPHI'EE LEQUOR- Application filed February 29, 1928, Serial No. 258,118, and in Germany August 16, 1%2'7.

My invention refers to the production of waste sulphite liquor and more especially to 'means whereby in this production pure car bon dioxide can be recovered as a by-product.

Hitherto sulphite liquor for use in the treatment of cellulose is produced in such manner that the gases of combustion of sulphur or burner gases, being products of calcination of pyrit s, after having been cooled down, are conducted through towers in countercurrentto water trickling down in these towers, which are moreover filled with pieces of lime stone or dolomite. The towers have also been replaced by troughs. Now in view of the fact that the burner gases only contain about 8 to 10 per cent per volume $0 the gases of combustion of sulphur not more than to 18 per cent, and that in producing the ovor-acid sulphite liquors, 3 volumes sulphur dioxide correspond to only 1 volume "arbon dioxide produced, the contents of carbonic acid in the waste gases is so low as not to allow a commercial extraction. Therefore the large quantity of carbonic acid, which might be recovered in pure state as a cheap by-product in the manufacture of sulpliite liquor, is lost altogether. In those cases, where the carbonic acid is extracted from the gas mixture by absorption in water under 5 high pressure, the use of carbonic acid contained in lime kiln gases, which contain about per cent per volume 00 is far more preferable.

In order to recover carbonic acid in the sulphite liquor production in a commercial manner, the process must be so conducted that the carbon dioxide is not separated from the exhaust gases, but the sulphur dioxide must already be separated from the other gases accompanying same in the beginning of the operations. Inasmuch as the solubility of sulphur dioxide in water is more than times greater than that of carbon dioxide the absorption of sulphur dioxide and separation irom the other gases only requires a little part of the expenditure which would be required for the separation of carbon dioxide. Therefore the new method based on r these facts is distinguished from the methods U hitherto used in that the gases containing S0 are not caused to act directly on the carbonates, but that at first a watery solution of sulphur dioxide is prepared, the percentage of which sutfices for furnishing after dissolution of lime stone or other carbonates in this solution under development of carbonic acid a sulphite liquor of sutlicient strength or at least a liquor which is strong enough to allow being subsequently brought to the required percentage of $0 by the sulphur dioxide gas escaping from the boilers. it

Inasmuch as the sulphite liquors for the treatment of cellulose must have a total con tent of d to 5 per cent of sulphur dioxide, and as he carbon dioxide gas on being developed still carries away a considerable percentage of S0 the manufacture of full-grade sulphite liquors requires a watery solution containing about 5 to 6 per cent sulphur dioxide. Now this percentage cannot be obtained by simply absorbing the burner or sulphur coinbustion gases in water. For obtaining a solution having such a high percentage of sulphur dioxide, either the gases must be absorbed under pressi re or SO must first be produced in any suitable manner and the gas must then be caused to be absorbed in water.

The pressure to be used for the absorption in order to obtain a sufficiently strong solution is inversely proportional to the contents oi SO in the gases to be operated upon and to the temperature of the absorption water. It is the lower, the higher the S9 contents of the gases and the lower the temperature of the water. lVhen operating with gases of combustion of sulphur rich in S0: and with cold water, a pressure of 2 to 3 atins. will sultice, while with burner gases of pyrites about i to 5 atms. are required.

In compensation for this expenditure in energy not only the sulphite liquor produc tion such is greatly simplified, but also a carbon dioxide substantially free from other gases is obtained. Instead of the very high lime stone towers at present in use the production of sulphite liquor according to the present invention only requires very simple and. comparatively small apparatus, ,u'ih as illustrated diagrammatically by way of example in the drawing, this apparatus being Cir adapted for use in carrying out a continuous operation.

Referring to the drawing, l 1 and A; are two iron reservoirs, the inner walls of which are covered with lead, and o, and G are manholes for filling in pieces of lime stone, which rest on the perforated double bottoms 7L; and 7: (1 (I: are pipes provided with valves, through which the solution of SO: from the absorption under pressure 'ran be admitted either in the reservoir A or reservoir A Pipes 0, and c serve for lraining the reservoirs and for coiulucting thy finished liquor to the tanks such as l. (ln the solution of sulphur dioxide entering a reser'ioir, a vigorous i'levelopiuent of carbon dioxide gas will take place, this gas being carried througpipes f, or f; to an absorber B which serves for absorbing any 5th, vhich may be 'arried away by the tarbon dioxide. This comparatively small absorben which has to provide room only tor l/Qtlth to l/-ltlth of the gas volume which had hitherto to be accommodated in the absorption towers may either be tilled with pieces of lime stone or, it it is desired to avoid the retillingr, with colic or some acid-proot material. Water supplied to the absorber B by means of the sprinkler pipe r/ and all the sulphur di is here extracted from the carbon (ll( xi le egas. The pure arbou dioxide (817215195 through pipe h into a amber in, tilled with a solution of bicarbonate, escaping lixn the washer through pipe 0 into a someter p.

In order to produce the carbon dioxide in an uninterrupted stream, the preparation of the sulphite liquor is carried out in the reservoirs A, and A alternately. lvhile one of the reservoirs is in operation, sulphite liquor is exhausted from the other one, fresh lime stone being" tilled in, if l'itPt'OHL-Zlil. 'lhe solu tion escaping from the absorber B can be conducted either to the rez-ieryoir A, or to the reservoir A: as desired through pipes f or f,. respectively.

Instead of producing a solution oi sulphur dioxide sullicientiy strong tor the preparation of the sulphite licpiors, I may also use pure St) gas for the production of pure carbon dioxide, the 510 being introduced into an apparatus tilled with a suitable carbonate and water or beinc r'onducted in eountercurrent to water tric l'u r down a tower tilled with lime stone. To this end the sulphur dioxide must first be expelled from its watery solution or must be prodiu'ed in pure state in some other way. Such process can be carried through in a commercial manner only wh re fresh or exhaust st 2am ayailable at low cost. ()n the other hand the process with solutions rich in Lit 2 and obtained directly by absorption merely requires power for compression, which frequently available in natural sources of energy without r quiring any expenditure for coal. The power consumption can be limited to a minimum, for the pressure of the exhaust gases is utilized again for the compression, n'iore, especially, it these gases are reh rated before expanding in the engine, for instance by the heat of the sulphur burners or by some, other exhaust heat, which is a 'ailablc tree of cost.

\Vhen manutzurturing a sulphitc liquor such as required for use and having a content of lime between 1 and 1.2 per cent about 7 to S kgs. pure carbon dioxide can be re covered as a by-product per cubic meter oi liquor. This carbon dioxide can either be utilized for special purposes, For instance for i a precipitation of bicarbonate in the manutacture of soda according to the ammonia proce:-:s, which does not require any energy and does not i'urnish ny exhaust gases, or it can be liquefied or solidified by compression and can be sold in this condition. 5

Various changes may be made in the details disclosed in the foregoing specification without departing from the invention or. sa rificing the advantages thereof.

1 claim l. The method oi producingsulphite lil uor and pure carbon dioxide comprising extra ting a gas containing sulphur dioxide with water under pressure for the recovery ol" Ht), from said gas, acting with the S0,,- solution thus obtained on a decomposable arbouate and collecting the carbon dioxide gas.

The method of producing sulphite liquor and pure 'arbon dioxide comprising extracting! a gas containing sulphur dioxide with water under pressure "for the recovery of SO: from said gas, acting with. the SO solution thus obtained on a decomposable carbonate, collecting the *arbon dioxide gas and washing same to remove the sulphur dio; oxide still admixed to it.

3. The method of producing sulphite liduo and carbon dioxide which comprises ahsorbing sulphur dioxide in ater under pressure to term a concentrated solution oii sul- 11o phurous acid, subjecting a decomposable carbonate to the action of the l'efilllilillg solution, and collecting the resulting gaseous and liq uid reaction products.

4. The method of producing sulphite liqnor and carbon dioxide which comprises dissolving: sulphur dioxide from a mixture of gases with water under pressure to term a comrentrated solution of sniplmrous acid, subiectin r a deerni'iposable carbonate to the action of the resulting solutioin and collecting the resulting gaseous and liquid 1' aictii n products.

In testimony whereoi I allix my signature.

MAX ozone raronoa 'scaiioanni. 12: 

